The present invention relates to a vehicular infrared light radiating lamp intended to be mounted on a vehicle for radiating infrared light forward of the vehicle, and more particularly relates to a vehicular infrared light radiating lamp used in common with a CCD camera having up to a near-infrared sensitivity.
A lamp of this type is constructed by arranging a visible light source and a parabolic reflector within a lamp chamber defined by a lamp body and a front lens. An infrared light transmitting filter, namely, a filter which reflects visible light components and transmits infrared light components, is formed over the entire surface of a glass plate disposed between the light source and the front lens with the entire front opening portion of the lamp chamber covered by the filter such that all light source light directed toward the front lens is transmitted through the infrared light transmitting film. Visible light components of the light source light reflected by the reflector of the lamp are cut when passing through the infrared light transmitting film while light composed primarily of invisible infrared light is emitted forward from the front lens.
The infrared light radiating region forward of the vehicle is sensed with a CCD camera having up to near-infrared sensitivity mounted on a front portion of the vehicle. The output of the camera is processed with an image processing device so as to produce a visual display on a monitor screen inside the passenger compartment of the vehicle. The driver is then able to confirm the presence of objects such as persons, lane markers, and obstacles in the distance on the monitor screen, which displays the field of vision in front of the vehicle.
The spectral characteristics of an infrared light transmitting filter for the above-described conventional infrared light radiating lamp are shown in FIG. 11. As shown by diagonal lines in FIG. 11, visible light (red light component) with a long wavelength of approximately 700 to 800 nm cannot be completely cut with the infrared light transmitting filter, and thus some visible light (red light component) passing through the infrared light transmitting filter together with the infrared light is also directed to the front lens. This portion of visible light (red light component) is emitted from the front lens together with the infrared light, so that the front lens emits red light to some extent and appears to a viewer as being lit red. This causes a safety problem in that the infrared light radiating lamp, which is mounted at the front portion of the vehicle, can be mistaken for a tail lamp or a stop lamp.
As disclosed in Japanese Patent Application No. 2001-205708, filed Jul. 6, 2001 (the “prior application”), the inventor earlier proposed a solution to this problem in which, by guiding a portion of light source light to the rim portion of the front lens without passing through the infrared light transmitting filter so as to emit white light from the rim portion of the front lens otherwise lit red, the red-colored light emitted from the lamp is diluted to the point where it become inconspicuous. This technique has been confirmed as effective in repeated test results.
As disclosed in the prior application, for example, as shown in FIG. 12, a light source unit incorporating a convex lens 4 mounted via a tubular lens holder 3 is provided forward of a reflector 1 on which a bulb 2 is mounted. An infrared light transmitting film 5 is formed on regions other than a rim portion of a rear surface of the convex lens 4, and an infrared light transmitting film-free region 6 is formed around the rim portion of the rear surface of the convex lens 4. By emitting from the convex lens 4 an infrared light beam L1 from which visible light has been cut and emitting a visible light L2 from a convex lens rim portion 4a, the convex lens rim portion 4a emits white light such that the red light emission color of the convex lens 4 is diluted.
However, light with a relatively high energy density including direct light from the bulb 2 and reflected light from the reflector 1 and the lens holder 3 is directly incident on the infrared light transmitting film-free region 6 and emitted from the convex lens rim portion 4, thus creating the risk of creating light which causes a glare effect. Also, by increasing the area of the infrared light transmitting film 5 (i.e., narrowing the infrared light transmitting film-free region 6) formed on the rear surface of the convex lens 4, it is also possible to adjust the amount of visible light emitted from the convex lens rim portion 4a such that it does not create glare. However, such an adjustment is not so simple because the reduced light emission reduces the effect of diluting the red light emission.
The inventor considered that if the energy density of the visible light emitted from the convex lens rim portion 4a ere reduced glare would not be created. As shown by a broken line in FIG. 12, a light shielding member 7 was provided on the inner side of the lens holder 3 so as to cover the rear of the convex lens rim portion 4a (infrared light transmitting film-free region 6), and tests were repeated to confirm the effect thereof. As a result, it was confined that that the light emitted from the convex lens 4 did not appear red in color and glare was not created. The present invention is based on this discovery.